Gifford Miller vs AR5 (FOD) Reconstructions

Miller et al (GRL 2012) url has attracted much recent attention for its argument that volcanism can account for the MWP-LIA transition. In my opinion, it is important for another reason, a reason not mentioned and apparently not noticed by the authors themselves. It offers a highly plausible re-interpretation of Arctic varve series, an interpretation that, in effect, stands the temperature interpretation of the important Big Round Lake, Baffin Island varve series on its head. Arctic varve series, including Big Round Lake, have become a mainstay of temperature reconstructions used in AR5 (FOD) and likely to be used in AR5 (e.g. Kaufman et al 2009) and Miller’s interpretation of varve data impacts multiple “new” AR5 studies. CA readers are familiar with climate scientists having trouble with the orientation of varve data e.g. the use of Tiljander’s varve data in Mann et al 2008-2009 (the latter frequently cited in AR5).

Over the past few years, Miller and associates have radiocarbon dated mosses at 90 sites revealed by receding Baffin Island glaciers, observing a concentration of kill dates in the late 13th century and again in the early 15th century. This is interesting and useful new data that is helpful to disentangling the climate history of the area. They interpret the lack of kill dates in the MWP (from ~950-1250) as due to relative warmth, resulting in recession and/or absence of the small Baffin Island glaciers:

Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD.

They interpreted the lack of kill dates from 1450 to the late 20th century as due to continuous ice cover until recent glacier recession. See their Figure 2C, excerpted in the top panel below:

Their Figure 2D (the bottom panel of the above graphic) is a smoothed version of varve thicknesses from Hvítárvatn, a proglacial lake in Iceland. Juxtaposing the information from kill dates with varve information, Miller et al concluded that the narrow varves from 950-1250 corresponded to glacier absence (or recession), indicating relative warmth, while the wider varves in the Little Ice Age showed the existence of active glaciers, indicating relative cold. Miller et al:

Baffin Island kill dates define abrupt and sustained summer cooling in the late 13th Century, which is matched by the start of a centennial trend of increasing Hvítárvatn varve thickness (Figure 2d), consistent with our predictions. A second abrupt increase in varve thickness in the 15th Century, and continuously thick varves through the following century, is consistent with persistent ice-cap expansion in the Canadian record at the same time. Hvítárvatn varves attain their maximum LIA thickness in the late 19th and early 20th centuries, decreasing again in the late 20th Century as Langjökull receded.

The picture, thus far, is consistent with the “traditional” perspective on the MWP and LIA – unsurprising since Baffin Island and Iceland are within the heart of the region conceded even by opponents. Miller et al argue (passim) that modern warmth is greater than medieval warmth. However, while the authors undoubtedly believe this, this point is made more as a genuflection than as a central focus of the article.

Varves of Baffin Island

However, this picture differs sharply from recent temperature reconstructions using Baffin Island varve data. For example, Thomas and Briner 2009, writing about the Big Round Lake (Baffin Island) varve series, reported that the period 1400-1575, rather than being a period of intensified cold with a “final pulse of ice-cap growth (as Miller et al concluded), had stated that it was relatively warm:

The warmest pre-twentieth century period in this 1000 year record, 1375–1575 AD,

Their temperature reconstruction, rather than interpreting narrow 11th century varves as evidence of warmth (as Miller et al 2012 did), concluded that the 11th century was exceptionally cold (despite the historical traditions.) This temperature reconstruction has been widely used in recent multiproxy reconstructions.

In the figure below, I’ve plotted the Big Round varve series on the same scale as the Hvitarvatn varve series, showing some important similarities.

For example, both the Big Round varve series and Hvitarvatn varve series show relatively thick varves in the 1400s and 1500s, with a local minimum in the late 1600s, then strong increases through the 18th, 19th and 20th century, perhaps tailing off a little towards the end. Despite this seeming similarity, opposite conclusions about the temperature implications were drawn by authors of the two series.

Thomas and Briner 2009 had interpreted the varve thickness increase at Big Round Lake in the 15th century as evidence of warmth, whereas Miller et al 2012 had interpreted a seemingly similar increase at Hvitarvatn as evidence of increasing cold.

In the 11th century (critical for medieval-modern comparisons), Miller et al 2012 interpreted narrow Hvitarvatn varves as evidence of glacier recession and/or absence i.e. local warmth, whereas the Thomas and Briner reconstruction (applying a postulated linear relationship between varve thickness and temperature) deduced that the MWP was very cold in Baffin Island. (This conclusion was not articulated or discussed in Thomas and Briner but is inherent in their reconstruction.)

Polissar concluded that local glaciers in the Venezuelan Andes had been absent in the MWP, but had reformed in the Little Ice Age (hence the different character of the sediments) prior to receding with increased warmth in the 20th century.

In this example, there was increased glacier activity in the Little Ice Age, resulting in more iron minerals in the sediments, a phenomenon seemingly analgous to Miller et al’s attribution of increased varve thickness in the LIA to increased glacier activity.

Two Factors?
The recent articles on varves underpinning the AR5 citations (e.g. Kaufman et al 2009 and its underlying studies such as Thomas and Briner 2009) attempt to interpret varves solely in terms of temperature. Most of the articles show positive correlations between late 20th century and varve thickness. Narrow varves (of MWP type) are not observed in the calibration period. This requires extrapolation of a relationship established over thick varves to the perhaps different circumstances of thin varves – a rather adventurous extrapolation of the sort that is typically discouraged in statistical literature.

There is considerable older literature on varves, principally in connection with LGM deglaciation. There is a prominent varve outcrop (see Tufts varve webpage here) about half a mile from my house. (The varves were re-exposed last year during straightening of Pottery Road). In the older literature on the LGM e.g. Agterberg and Banerjee 1969, varve thickness was held to depend on proximity to the ice front:

Both the silt (summer) and the clay (winter) layers in a varve couplet show an approximately exponential decrease in thickness away from the icefront. This trend is more conspicuous in the sill

When the Laurentide ice sheet had sufficiently receded, so did the varve series. When Miller et al 2012 attribute the narrow 11th century varves to glacier recession/absence, it seems to me that they are observing more or less the same phenomenon, though on a much diminished scale.

Thus, as Miller et al 2012 imply, thin varves could result from either glacier recession/absence (cumulative warmth in the 11th century) or relative cold (in the late 17th century) – confounding efforts to reconstruct past temperatures using a linear relationship to varve thickness.

Efforts to reconstruct past temperature using simplistic linear relationships to varve thicknesses (as in the studies applied in Kaufman et al 2009) had already struck me as problematic though, prior to Miller et al 2012, the precise problem had not been diagnosed. In my opinion, Miller et al 2012 provides substantial support for rejecting the interpretation of narrow 11th century varves as evidence of medieval cold (the Big Round temperature reconstruction) and requires analysis of the effect of this (and similar data) on downstream multiproxy reconstructions.

Postscript: I’ve managed to write this post without referring to Kortajarvi sediments other than once in passing. Mia Tiljander had interpreted narrow varves as evidence of medieval warmth and wide varves as evidence of the LIA. The data was used in opposite orientations in the corrigendum to Kaufman et al 2009 and in Mann et al 2008-2009, with Raymond Bradley ironically being a coauthor of both studies. In Mann’s recent book, he argued, in effect, that it doesn’t matter whether the Tiljander data is used upside down or not in Mann et al 2008 and 2009. I disagree, but, regardless of its orientation “matters” in the Mann et al articles, it seems reasonable to expect scientists in the field to develop consistent scientific interpretations of narrow 11th century varves.

94 Comments

If the warm/narrow vs cold/narrow is correct and with it the postulate of volcanism as the precipitant of the LIA, then why did earlier known pronounced volcanic activity in the middle of the MWP not do the same thing?

Here is a very good paper on the subject of these eruptions and interestingly enough while there is a correlation with the beginning of the cool period associated with the 1257 unknown volcanic explosion, there is no follow on sustained activity that would further drive the system.

Interesting as well the Baitoushan volcano from ~1029 AD has a larger known effect on climate as it is referenced by H.H. Lamb as being the cause of the winter that resulted in the freezing of the nile. Baitoushan and its temperature effects are shown in the above paper as well as being greater than the 1257 event, at least in England, though its sulfur content was less.

Though other sources put this eruption in the late 900’s the GISP data is pretty solid. I first learned about this volcano from none other than Biffra in the Climategate-1 emails.

If the 1257 volcano was supposed to have this effect, why not the earlier baitoushan eruption?

Steve: I would prefer not to discuss the history of volcanism or its impact, neither of which is discussed in this post, though interesting topics. I’m not familiar enough with the details to comment. This post is about something different: the interpretation of varve thickness series, an important and thus far undiscussed issue in several AR5 temperature reconstructions.

Sorry, I thought that the entire premise behind the Miller et al argument as the volcanism is the culprit for the MWP to LIA transition rather than any other influence (i.e. solar) and were using the varve’s as their proxy. If there is no sustained vulcanism in the GISP2 record that would provide the means to interpret the varve data, then it would tend to indicate that the warm thin varve vs cold thin varve cannot be explained by that source.

Am I off base here?
Steve – the Miller argument is about volcanism. However my interest in this post is in the interpretation of varve time series – a different issue.

Upon further research I think that I understand where you are going with the varve interest. Pinning down varve thickness as a direct temperature proxy has the same level of certainty as ascribing tree ring thickness to temperature only. Unless you can disentangle the rainfall in those areas from temperature, there is no way to ascribe varve thickness to temperature.

The growth of glaciers, like that of trees, apparently depends upon more than temperature. As measured by the ERS-1 and -2 satellites from 1992 to 2003, Greenland’s interior ice was increasing at the rate of about ~5cm (2 inches) per year, on top of an isostatic uplift of about 0.5cm per year. When the GRACE pair were launched in 2003, this immediately became a catastrophic loss (despite GRACE’s problems).

At the time, precipitation was involved to explain the decade-plus of rapid ice growth, despite the assertion of increased warmth. That has a recognizable element of truth, or at least plausibility, and its application here suggests the connection between precipitation rates and glacial advance. Certainly even in very cold periods, dry weather would not much advance glaciers.

One of the graphs above denotes “wetter” rather than “colder” which makes sense. But the upshot seems to be that interpreting varves as proxies for glacial advance as proxies for temperature is complex — and we apparently have no basis yet for much confidence in the putative temperature reconstructions.

In this post, I’m not discussing or contesting the issue of whether the growth/recession of small Baffin Island glaciers is primarily due to temperature. Miller et al argue that growth/recession of Baffin Island glaciers is a proxy for temperature (whether the same is true for Killimanjaro is a different issue). The issue in this post is the validity of proglacial varve thickness as a linear proxy for temperature.

But to your point: Glaciers mostly depend on winter precipitation and summer temperature.

Regarding ERS-1 and ERS-2
as a remote sensing analyst I can tell you the resolution on ERS’s radar altimeter is not sufficient to be able to detail loss in dynamic regions (coastlines/steep slopes). This is detailed in the literature extensively. Thomas et al (2007 or 2008, I forget) shows how ERS significantly underestimates ice loss due to the issues i’ve mentioned.

The varve thickness is affected both by temperature (and/or moisture) as they affect the glacier AND how far the location is from the glacier terminus over time. It is 3 variable problem, where it is just assumed in order to make it a proxy that it is a 1 variable problem. Where have I seen that before?
Steve: yup.🙂

Whoever killed the animals was used to living in squalid conditions. The bone-littered earthen floors had been spread with an insulating layer of twigs that attracted mice and a variety of insect pests. Study of the farms’ ancient insect fauna revealed the remains of flies. Brought inadvertently from Europe, the flies were dependent for their survival on the warm environment of the Norse houses and on the less than sanitary state of the interiors. Radiocarbon dating of their remains revealed that they died out suddenly when these conditions ceased to prevail around 1350, presumably when the structures were no longer inhabited.

985 to 1350 is in rough agreement with the warm period shown in the varves from Hvítárvatn.
Steve; better to say the period of relatively thin varves.

Polissar et al have a 2006 abstract of related USA work stating ” Analyses include AMS radiocarbon dating, sedimentology studies, pollen and diatom assemblage investigations, magnetic susceptibility, geochemistry and stable isotope measurements (C, N, and O) on a series of cores from 7 lakes and 2 bogs.” A quich search also shows a 2005 Venezuela paper noting “Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation.”

The use of magnetism can be complicated. It is customary to measure not only magnetic susceptibility, but also remanent magnetisation. Misinterpretation can result by omission of the latter. See for example Reynolds et al for some of the complications, as well at the contemporary dynamics of geochemical species with magnetism. http://www.mendeley.com/research/freeze-coring-soft-sediments-in-tropical-lakes.

I’ve not had time to study the relevant papers in detail yet, so this is merely a precautionary comment.

Miller refers to Koerner 2005 to establish that the primary driver of glacial growth or decline is summer temperature. This value looks more like melt loss rather than the complete picture of snow & ice build-up minus melt loss. To be certain, we’d have to look at Koerner 2005.

Miller also refers to Larsen et al. 2011, a relatively new publication, for rational on varve thickness and glacial ice flow and glacial flow apparently a good proxy for temperature. This is more dubious than the Koerner 2005 idea and Larsen 2011 deserves a good examination.

The key to the varve thinkness appears to be because Hvítárvatn is predominantly a glacier-fed lake. Whether or not AR5 has it correct would depend on this characteristic matters and the validity of the referenced research papers. Of course, AR5 might reject Larsen 2011, and go with Leeman and Niessen, 1994 instead.

The relevant quotation on Larsen et al, 2011
[quote]
However, on decadal and longer timescales it is glacier power, the amount of work a glacier accomplishes on the landscape, that controls varve thickness. Thus, supra-decadal changes in Hvítárvatn varve thickness track the intensity of Langjökull erosion, and serve as a proxy for ice-cap size [Larsen et al., 2011].
[/quote]

Your comment on Mia Tiljander’s work implies that it stands alone, yet if you read the dissertation (available in English) it is only one of a series of studies of the varves in various lakes in Finland, and her findings are consistent with those of others in different lakes.

> [Tiljander et al’s] findings are consistent with those of others in different lakes.

Yes, that’s by and large (though not entirely) true. And Tiljander et al’s interpretations of temperature’s influence on varves were qualitative and rather vague. So, in the context of this post, can you be more specific in terms of the point you are making and the work that supports it?

“If a data series is indeed a proxy for temperature, it should have characteristics that indicate that it’s a proxy for temperature. One would think that an obvious statement like this would be readily grasped.

In that regard, there are data series for Southern Finland that do appear to be proxies for temperature. See the figure of temperature reconstruction from T.P. Luoto’s dissertation on fossil Chironomids from Lake Hamptrask (here; search for “I just looked at Fig. 14″). It’s widely accepted that the Little Ice Age extended to Scandanavia — and a downward excursion in Luoto’s Chironomid-derived series can be discerned for those dates. If there is an analogous temperature-derived signal in LS or DS [in Tiljander03], it is a subtle one.”

Locations fairly close to rapidly retreating glaciers experience increased varve thickness due to the high levels of suspended silt in the run-off; as the glacier receeds from this location, the varve thickness decreases since the run-off has less of a chance to make it back to the baseline location. The locations where varve thickness remain wide occur progressively northward of the baseline location as the glacier receeds. Should deep cooling take place, all varve-forming activity may diminish. Locations far to the
south of the glacier may see thin varve-forming activity either due to higher temperatures, deeper cooling or neither, since the location is too far from the glacier.
Locations deep under the glacier show little varve-forming activity. The situation if far from being the simple–varve thick=hot, varve thin=cold. Good analysis, Steve, as usual.

Is there a gradation in the size of particles deposited at a site depending of the distance from the glacier. That is are larger particles more likely to be deposited than the smaller. If so the larger particles are deposited sooner. Would it be possible to use this to determine if the glacier is receding or advancing. So the change in dimension over time for particles at a given site could be an indication of the progression or recession of glaciers. Is there any merit to this idea?

Another thing to consider is that glacial terrain can become erratic, with drainage patterns shifting over time as terminal and lateral morraines are established, erode, and are overridden later. Flow of water could get cut off from the lake being studied at one time and then reestablished later without that meaning anything about temperature.

This is very true. Proglacial drainage patterns are often very unstable and can change abruptly with both retreats and advances of the glacier front. In Sweden where varve-research originated there is even a special word (“tappningsvarv”) for exceptionally thick varves connected with sudden draining of proglacial lakes.

One would, a prior, suspect that surface mineral layers exposed to an oxygen rich atmosphere would have quite different chemical signatures than ones held at the based of an anaerobic ice filled lake.
I find it odd that the chemistry of the layers has not be extensively investigated.

Varved glacial sediments are typically deposited well in front of a glacier and in aerobic conditions. We aren’t talking of Lake Vostok here. As a matter of fact glacial meltwater is usually quite well oxygenated.
As a matter of fact I can’t remember any evidence of varved sediments being deposited (and preserved) in subglacial lakes in the northern hemisphere, though I do know of cases where this has happened in subglacial caves in Norway.

In some articles about W Canadian lake varves discussed here a few years ago, the correlation between thickness and temperature was supposed to be different depending on whether the lake was glacier fed or snow fed:

If glacier fed, a warm year would cause high summer runoff and thick varves. But if snow fed, a cold year would cause more precipitation to be in the form of snow, resulting in a particularly voluminous spring thaw and thicker varves.

Things must get complicated if there was a glacier feeding the lake during the LIA, but none now or during the MWP. I gather these two are glacier fed?

Now it looks like the distance from the glacier face is a big factor as well. No easy answers.

I’ve added a plot to the main post showing several indicators from the Big Round data set: varve thickness, magnetic susceptibility and biogenic silica. Varve thickness and mag suceptibility track one another closely (i.e. more iron minerals in the higher runoff varves; biogenic silica unrelated to either.) The data archive for biogenic silica is either incomplete or Thomas and Briner didn’t run this test on their longer core.

The whole point of publishing a paper is to BEGIN discussion within the scientific community. The idea that scientific discussion should only be carried on in journals is one of the great corruptions of climate science. What do you think graduate students do all day?

When a Ph.D. student my prof would invite visitors to our group. He would sort of debate with them, sparring (he was a combative sort, earned college money boxing) and we would join in, debating the issues of the day. Us students got points if we could keep up with the debate. Interestingly, the reaction to him was very similar to how some must feel about our host. He was a master at finding a weakness in an argument or data and would be the first to raise his hand after a seminar and ask a tough question. When speakers got up to the podium who weren’t totally prepared and saw him sitting there I saw some get pale and lost their train of thought.
So yes debate IS the point, but not everyone feels that way.

In his paper justifying the CERN CLOUD experiment, Jasper Kirkby used data from Polissar et al 2006 to show the correlation between Venezuelan glacier advances/recessions and Be10 & C14; graphs on page 3.

I’m often surprised by the correlation between various proxy series. Similar lows and highs even in tree rings. Climate variables are being recorded but we don’t know which or by what calibration function.

This post is an interesting find though which underpins the huge uncertainty in the field. Everything we read indicates the same thing. We don’t really know if these series are temp. They are interesting because of their correlation, but even the pro’s don’t know whether it should be interpreted +/-. A huge difference even by climatology standards.

I’m also often surprised that an unpaid individual has enough time to read so many of the papers in context. Even someone experienced with the various series requires a lot of time to read this stuff. Then to get the data, plot the data, grock it and write about it? !!

Ed_B, if our host is George Smiley then Karla must be an alias for the Team. We can only hope that this analogy holds until the end. I would pay for the privilege of watching the Team take the walk across the metaphorical foggy bridge into a future of a life in a safe house.

The punch line from Miller et al. is, in case you missed it, the following:

“From both the Canadian evidence (many sites became ice-covered in the late 13th Century and remained so until the past decade) and Icelandic evidence (consistently thick varves following the late 13th Century), we can conclude that multidecadal average summer temperatures never returned to those of Medieval times until the 20th Century. The 24 Canadian sites that became ice-covered _800–900 AD (Table S4) and did not melt again until the past decade demonstrate that multi-decadal average summer temperatures in Arctic Canada now exceed those of Medieval times.”

I quickly read the article and I pretend no expertise of the subject matter, but I get a distinct feeling that I am seeing conjecture piled on conjecture. I particularly like the hand waves to feedback to explain the lasting coldness.

I’ve bought the Kindle version for my iPod but haven’t got past the introduction. I want to try to approach it with an open mind, but he’s already spent several paragraphs crying into his onion, and I can only take so much at a time. Must be done though.

At this late date, only Alice-in-Wonderland defenses remain, as far as the use of Tiljander’s proxies by Mann08 and Mann09. But they’ve never been out of style. I’m reminded of this early one at Stoat, from 10/28/2009:

“[The sign going in is the point at issue here. If the sign going in is wrong, then the correlation has the same absolute value but the wrong sign, which means the series gets added back in to the reconstruction with the sign wrong twice, ie correctly. If by “the correlation is aphysical” you mean, of the wrong sign, then you are correct. BUt this is irrelevant -W]”

Ouch.

ISTM that errors are inevitable. What’s more important than “being right” is allowing for discussion of diverse interpretations. Miller’s view of varves in glacial lakes sounds reasonable, as does Thomas & Briner’s. It’s unlikely that both perspectives are broadly correct. That should be fine, as long as “the science” isn’t performed with quick-cure concrete. As was done in the case of Mann08 and its literature and blog spawn.

Mann also refuses to acknowledge that the NAS 2006 report recommended against the use of strip-bark bristlecones in temperature reconstructions. He misrepresents the report in his book as follows (emphasis added):

McIntyre also appealed to the conclusions of the 2006 NAS report to claim that our continued use of the very long bristlecone pine series was inappropriate. Yet this was a misrepresentation of what the NAS had concluded. The NAS panel expressed some concerns about so-called strip-bark tree ring records, which include many of the long-lived bristlecone pines. These trees grow at very high CO2-limited elevations, and there is the possibility that increases in growth over the past two centuries may not be driven entirely by climate, but also by the phenomenon of CO2 fertilization – something that had been called attention to and dealt with in MBH99 (see chapter 4). The NAS report simply recommended efforts to better understand any potential biases by “performing experimental studies on biophysical relationships between temperature and tree-ring parameters”. Such would be the focus of a paper published in PNAS by Mathew Salzer and co-authors the following year, demonstrating that the much-maligned bristlecone pines were good temperature proxy records after all, and those records supported the conclusion of anomalous recent warmth.

The quotation in the bolded sentence is from page 52 of the NAS report – it’s a recommendation for “tree ring science” in general. On the very same page, the report recommends against using strip-bark samples for temperature reconstructions : “While “strip-bark” samples should be avoided for temperature reconstructions, attention should also be paid to the confounding effects of anthropogenic nitrogen deposition (Vitousek et al. 1997), since the nutrient conditions of the soil determine wood growth response to increased atmospheric CO2 (Kostiainen et al. 2004). ”

Gavin Schmidt, a RealClimate colleague of Mann, understood the NAS report in the same manner as Steve when he wrote at that blog : “Some studies have suggested that such trees be avoided for paleoclimatic purposes, a point repeated in a recent National Academy of Sciences report (Surface temperature reconstructions for the last 2,000 years. NRC, 2006).”.

At risk of getting OT, I just note that in a proper field of study, reviewers and editors would not let one just make stuff up or use data which are suspect or worse (both Tiljander varves nd bristlecone falling in this category).

It turns out there’s a quicker way: apply the Highlight function to the passage, and if you log into your Amazon kindle account via the web browser the highlighted passage will be available under ‘Your Highlights’.

Kindle for the PC (which is free, and can have free copies of your other Kindle docs) allows easy copy and paste — and automatically appends the attribution cite. For example:

Consortium grants involve more than one institution. In a common situation the PI is at the primary institution and the Co-Investigator is at another university or, perhaps, in an industrial laboratory.

“Thus, as Miller et al 2012 imply, thin varves could result from either glacier recession/absence (cumulative warmth in the 11th century) or relative cold (in the late 17th century) – confounding efforts to reconstruct past temperatures using a linear relationship to varve thickness.”

I wonder if you could differentiate between the two by looking at the rates of changes in the varve thickness while considering the mechanisms of glaciation.

It seems to me that the conditions leading up to the period of glaciation a slow poderously inevitable drying (thinking of dry grasslands populated by Mammoths and/or Mastodons on the glacial verges (but probably not during the LIA ^u^)) versus the subsequent flash floody period leading out of glaciation.

While the mechanisms I suggest above are very cartoonish, I am sure a glaciologist could provide some experience… someone like say Tamsin Edwards over at “All Models Are Wrong – But Peter and Steve B. don’t want to give people the wrong impression”.?

What is the take away of this paper and its analysis here – for the layperson that is?

I see in Figure 2 graphs at the bottom that would visually appear to show a positive correlation between temperature and varve thickness with the temperature derived from a borehole temperature inversion. Both the borehole and varve proxies then show a divergence starting in the middle 20th century from what I assume would be higher temperatures in the instrumental record.

Tiljander had an opposite correlation and Mann (08) had the same- is that correct?

Anyway I reread Miller(12) in hopes of determining any implication (for me at least) of whether he had a different and mixed interpretation. What I excerpted below would tend to imply that the kill-dates, which are so very important to the conclusions of the paper concerning rapid advance of glaciers due to volcanism, are confounded by warming and cooling and therefore Miller resorts to varve thicknesses. The author then notes that the varve thicknesses can be increased on annual time scales by outlet ice melting as opposed to thickening varves by way of the grinding of the ice cap which would relate to the mass of the ice cap and colder temperatures.

“The lack of kill-dates between 950 and 1250 AD reflects either continued cold without new ice growth, or an interval of warmth, and widespread ice recession. To distinguish between these opposing interpretations, we turn to an annually resolved record of ice-cap growth from Iceland; no other record from Baffin Island contains unambiguous proxies at the necessary resolution. Outlet glaciers of Langjökull, a 950-km2 ice cap in the central highlands of Iceland, deliver erosional products via fluvial discharge to Hvítárvatn, the glacial lake immediately adjacent to the ice cap (Figure 1). The volume of sediment delivered by a glacier to an adjacent lake is a response to both year-to-year variations in summer weather and to longer-term variations in climate. On interannual timescales warmer (or wetter) summers are more efficient at delivering ice-erosional products to a lake, producing thicker annual laminations (varves [Leeman and Niessen, 1994]). However, on decadal and longer timescales it is glacier power, the amount of work a glacier accomplishes on the landscape, that controls varve thickness. Thus, supra-decadal changes in Hvítárvatn varve thickness track the intensity of Langjökull erosion, and serve as a proxy for ice-cap size [Larsen et al., 2011].

The response time of Langjökull outlet glaciers to abrupt summer cooling is approximately a decade and the estimated ice-cap equilibration time is _100 years (H. Björnsson, unpublished data, 1997–2011). Consequently, Langjökull outlet glaciers will begin to advance within a decade following abrupt summer cooling, although the ice cap will not attain its new equilibrium dimensions for a century. We therefore expect that times of abrupt snowline lowering derived from the Baffin Island kill dates should correspond with the onset of multidecadal trends of increasing varve thickness in Hvítárvatn.”

So we have an annual and decadal or longer responses of varve thicknesses to glaciers that appear contradictory with regards to temperature. Miller in the second paragraph evidently resolves that problem by using an unpublished work of the differences in the equilibration times of the outlet glaciers and the ice-cap. How does Miller then reconcile the graph he shows with the complicated picture he paints for the factors and lag times for varve generation and thickness. He does not because he is most intent on showing how volcanism that should have short term effects, vis a vis aerosol production, can have lasting effects through feedback. He shows the results of 500 plus years of a climate model from a volcanism input that he does not quantify in the paper proper. The graphed result shows a quick ramp down and lasting effect on temperature. Unfortunately the graph ends at 1700.

Climate science being climate science, I well could see this paper being used to show the varve thickness and temperature proxy as valid and at the same time showing that LIA was caused by volcanism that has cooled the climate until recently and could even imply that the warming to overcome that residual LIA makes that warming larger than we would have assumed without lasting LIA effects. The LIA computer model of 500 years shows a nice Mannian handle on the hockey stick. The divergence might be a bit of problem but it could probably be ignored or waved at.

On a second and third look at the 2 graphs at the bottom of Figure 2 Miller (12), I would have to say the varve thickness, in general, decreases with temperature and not increases as I stated in my previous post. I am not accustomed to viewing temperatures upside down. That relationship would be in line with Tijlander’s view. That situation would imply that the overriding factor, according to Miller, in increasing varve thickness would be the centennial increase in the ice cap mass. That has a 100 year equilibration period to temperature according to Miller and thus any calibration of varve thicknesses with the instrumental record would be complicated by that lag and further by the contribution to varve thicknesses from the outlet glacier on a decadal scale which is assumed to add more disposited material in warmers summers from melting ice. I guess on further reading this all ties back into what SteveM stated in his thread introduction.

I was clued in by reading the following excerpt from a review of Miller (12) linked at:

“To broaden the study, the researchers analyzed sediment cores from a glacial lake linked to the 367-square-mile Langjökullice cap in the central highlands of Iceland that reaches nearly a mile high. The annual layers in the cores — which can be reliably dated by using tephra deposits from known historic volcanic eruptions on Iceland going back more than 1,000 years — suddenly became thicker in the late 13th century and again in the 15th century due to increased erosion caused by the expansion of the ice cap as the climate cooled.”

I eagerly await the interpretations by climate scientists and AR5 of Miller (12).

I believe I saw a reference, perhaps from AMac, that the varve samples are x-rayed (to estimate the metal silicate content?). Is that an effort to distinguish between the deposits due to grinding (ice cap mass related) and the erosion due to ice melt? If so, do interpretations of the varve thickness and temperature relationships require the use of equilibration time constants for grinding and run-off melt?

There are lots of ways to analyze varved sediments — thickness, organic and mineral content, particle sizes, isotope composition, magnetic orientation… the list goes on. Depends what you think will get at the issues you’re interested in studying.

I summarized Tiljander03’s methods here; search for “the measurement of Thickness and XRD”. Some papers describing more complex analyses of Scandinavian varved sediments are listed here.

I asked this question before but received no answer. It would seem reasonable that heavier particles would fall out of a flow sooner than lighter. Is it accurate to say that the size of particles at any one location will be dependent of the distance of that location from the origin of the sediment. If the source is a glacier could the size of particles in each layer be an indication of the changing distance to the glacier as it advances and retreats?

Yes, this is clearly the case, all else being equal. More specifically, larger particles will stay suspended in water that is faster-flowing and with more-turbulent flow.

You can see that changes to the environment adjacent to where the core is ultimately taken can significantly affect something like particle size. For example, an outflow channel with a heavy sediment load can frequently change course (see “braided stream”). So a given spot might be much closer to rapidly-flowing water at one time than at a later time.

If the outflow travels down a steep slope to get from glacier to lake, a change in distance (as the glacier advances or retreats) might not matter much. Or the characteristics of the varves might not follow in any direct or obvious way from such changes.

These comments are made from general knowledge only. Hopefully, where mistaken, they will be corrected by a reader with relevant expertise.

>Yes, this is clearly the case, all else being equal. More specifically, larger particles will stay suspended in water that is faster-flowing and with more-turbulent flow.

Correct, assuming a reduction in slope and/or channel confinement with increasing distance from source. One of the defining characteristics of channel deposits is spatial variability in sediment size and composition. A product of continuous deposition-erosion-deposition episodes typical of channel processes.

In this case we are dealing with lake deposits, which have characteristic differences from channel deposits. Simplified: sediment transport occurs as either bedload (rolling/saltation) along the channel floor, or in suspension within the water body itself. Typically, bedload comprises silt-sized and larger sediments, and suspended load clay size fraction particles. Note that in this case, clay is defined as a size fraction, not as a class of minerals.

Waves arms. Where our ideal channel meets lake, flow expansion and reduction in stream power will allow deposition of bedload, coarsest first, finest last as some kind of delta. Suspended load will be carried into the lake water body and slowly fall out of suspension (Navier Stokes equation). Varve thickness will therefore be a function of supply, residence time, lake depth and turbulence (and probably more that I can’t remember).

Varvology and dendrochronology are essentially exercises in reverse engineering of natural processes. As such, the inherent weakness of reverse engineering applies: the more interesting a feature, the less likely it is to be properly understood, and the more likely it is to be a contingency of history. And there is a similar law for reverse engineers: the more confident you are in your reverse engineering efforts, the less likely you are to have ever had any conclusive confirmation that you were right or wrong. That confirmation step can be very humbling, in my experience. Fortunately for them, these paleovarvologists will never face that day of reckoning!

AMac, I’ll do these one post one per link. The first link is the one I had evidently recalled in my post above. From that link I received the distinct impression that the organic deposits were what was of interest and that it is those deposits that are judged to correlated with the annual summer climate. Is that correct?

It would appear from Miller (12) that one would want to use both the organic based and mineral based deposits; the minerals used for tracking the centennial ice cap mass changes and the organics for the annual/decadal climate. What do the investigators attribute the silica based deposits to in Tiljander?

AMac have you confirmed that Mann(08) did not realize that only 2 of the 4 proxies were independent of the others? That is a very serious breach of statistics and/or an indication of some sloppy/hasty work. When someone mentions one or two errors and weaknesses in Mann(08) I like to reply with the most comprehensive list of errors/weaknesses at my disposal. Have others noted this same problem and what it does to the degrees of freedom in calculating statistics?

AMac, I got the interpretation of the organic and inorganic layers from the excerpt below from the Tiljander paper. That explanation and the location of the lake of interest in Tiljander would appear to me to indicate that the varves in Miller(12) and those in Tiljander are from entirely different origins and thus require entirely different interpretations.

“The above-mentioned factors, the amounts of inorganic and organic matter, form the basis of the climate interpretations. Periods rich in organic matter indicate favourable climate conditions, when less snow accumulates in winter by diminished precipitation and/or increased thawing, causing weaker spring flow and formation of a thin mineral layer. In addition, a long growing season thickens the organic matter. More severe climate conditions occur with higher winter precipitation, a longer cold period and rapid melting at spring, shown as thicker mineral matter within a varve. However, it is difficult to make climatic interpretations at the annual time scale, but short-term changes (averaged over a few years) could be estimated.”

> [In Tiljander03,] organic deposits were what was of interest and that it is those deposits that are judged to correlated with the annual summer climate.

Yes, see your quote at 3:36 PM.

> have you confirmed that Mann(08) did not realize that only 2 of the 4 proxies were independent of the others?

Only rarely have Prof Mann, his co-authors, or his co-bloggers responded substantively to questions about Tiljander03-in-Mann08, so it isn’t easy to say much about the thinking behind their actions. My own interpretation is that they meant well, got in beyond their depth, adopted a tough-it-out policy, and have kept to it ever since.

> Have others noted this same problem?

I think Steve McI has pointed it out in passing.

> what it does to the degrees of freedom in calculating statistics?

I don’t know. Given the dependence of key conclusions of Mann08 on Tiljander, it may be material. But there’s so much amiss there, that DoF problems may fall into the “not even wrong” category.

> [The] varves in Miller(12) and those in Tiljander are from entirely different origins and thus require entirely different interpretations.

Yes, the contexts of the sediments are very different. No glaciers feed Lake Korttajarvi, obviously. There, mineral matter is contributed to varved sediments by erosion of soils within the mostly low-lying watershed (which includes a lakeside city). Tiljander and other authors have identified numerous potentially-confounding factors, including a pre-1800 fall in the lake level (IIRC), land-use changes (e.g. farming and peat-cutting), and, er, bridge reconstruction.

I interpret the passage from Tiljander03 that you quote at 3:36 PM as ‘informed and reasonable speculation.’ In other words, their hypotheses are not tested and not quantified. Note that “more organics” comes from “wetter and warmer summers” and that “more minerals” comes from “wetter and cooler winters.” If temperature was the most important factor, Darksum would tend to have an inverted relationship to Lightsum. If precipitation was primary, we would expect the correlation to be direct. Graphs of the two show a more direct relationship (Mark I eyeball).

Hi Steve
Will you do a post on the Heartland documents that have recently been released? While you are at it, maybe also one on Patrick Michael’s alteration of Schmittner’s (2011) graph. I only ask in the interest of balance, because up to now you seem to be solely concerned with auditing climate science, not the outputs of climate sceptics. This gives the unfortunate impression that you are not even-handed. Thanks.

This is Steve’s blog and he can post on whatever topic he wants. Given the name of the blog, it is perfectly reasonable to expect him to audit climate science and not climate skeptics. He is under no obligation to address any topic that you (or anyone else) think he should. If you think this somehow makes him less than even-handed – well, that is your problem not his.

I won’t presume to answer for Steve, but for me personally, it is not a coincidence.

As long as the use of “pal review” remains endemic in mainstream climate science, publications containing errors, exaggerations and misrepresentations will continue to appear regularly in the literature. Once such papers have been published, there seems to be a distinct reluctance on the part of that community to explicitly correct those errors, possibly due to a fear of damaging the “cause” and/or the reputations of their fellow members of the “consensus”. With the amount of such material out there, it doesn’t leave much time for auditing anything else.

However, should you possess any scientific talent or knowledge, I would recommend that you could take on the role you are suggesting yourself. Blog sites are available for free – WordPress is a good choice – so you can publish whatever errors you may find. This would help to “even the playing field” and correct any imbalance that you apparently think exists in the audit process.

By the way, just for the record, have you ever posted comments on RC or other consensus blogs advising the same “even-handedness” when papers by “sceptical” authors are being discussed?😉

There are plenty of sites which “discuss” those works you mention in a critical manner, but only a very small number which discuss those studies which are shaping world policy. The latter rarely get the scrutiny they need.

There is nothing in the previous comments which provides any information about our host’s state of mind or his intentions. Your baseless (and ignorant) non sequitur is common trolling which deserves to be relegated to the used electron bin.

I would suggest unless future comments are directed to the topic in the head post, they might be considered as OT.

The skeptics aren’t controlling world opinion on AGW through the IPCC and pal reviewed science, so I wouldn’t be focusing my attention on them either.

There would be no need for Steve to even do this if the mainstream climate scientists/advocates/communicators he has had to audit would stop being sneaky and deceptive, and would archive the actual data and code that they actually used, when they used it, without needing to be prompted.

It would also be nice if they would stop crying and whining. I know nothing of science, but I do know that it has to be checked and verified many times before it can be the basis of worldwide public policy.

AMac, I would think that while the Miller(12) varve thicknesses are of a different origin than those from Tiljander, I would wonder whether the Miller varves would not have some confounding of the inorganic silicates assumed in Miller to be related to ice cap mass with the source that Tiljander relates to winter temperatures. That might depend I would suppose on the Miller varve deposits being subjected to spring flooding that in turn would depend on winter snowfall. Maybe the climate and location differences preclude the confounding.

Whether the use of 4 proxies in Mann(08) in the place of two independent proxies, in my mind, would have less to do with whether it significantly changes the results the analysis (doing that properly means taking all the errors in methodology together and not one at a time) but rather what it says about how well the authors understood the physical basis of the proxies used in their reconstruction.

This might be relevant to your discussion here, and if not relevant, maybe interesting anyhow. A couple of years ago on my blog I did a post on global warming alarmist Stephen Schneider’s (now deceased) appearance on the 1970’s TV show In Search Of…. In this case the subject matter was: In Search Of…The Coming Ice Age. I posted the video due to the irony of Schneider’s appearance on his show compared to his pronouncements in more recent years. Anyway, a much younger Gifford Miller appeared on this show, and they filmed his appearance on Baffin Island, and he discusses that evidence on Baffin Island indicates a cooling and drying trend for the last 3,000 years, etc.

Here’s the segment (1st of 3) that features Miller (his appearance starts at 5:30 in the video)…

…and for all three segements of the show for those intersted, it is here on my blog…

I’m an archaeologist evolved in a long term research project centered on the American Southwest; more specifically the late 13th century collapse of Salado culture of the central Arizona Upland, its brief reorganization in the early 14th century and its final systems failure and disintegration around 1400. Several years ago we published a paper (2001 Exploring the Gila Horizon. In Kiva 66(4)) that demonstrated a strong case for the rapid abandonment and reoccupation of much of the Tonto-Globe area with similar impacts on much of east-central and southeast Arizona, all centered upon 1300.

Herein, we employed a number of ceramic seriations each focused on discrete geographic/traditional areas. Collectively we sorted the available decorated ceramic data accorded to basic ware types from excavated contexts recovered at several hundred late prehistoric sites. Overall this sample included only assemblages from habitation sites occupied for at least several decades between 1100 and 1400. The general analysis of these data was based simply upon dominant ware types found in each geographic/traditional area.

In each of the various geographic/traditional areas this methodology identified virtually the same pattern; an extreme bifurcation separating those settlement dominated by Whitewares occupied before 1300 from those established after 1300 and dominated by either Salado Redwares, White Mountain Redware or Northern Mexican Polychromes. There was virtually no overlap. For example in the Tonto-Globe area, assemblages from about a hundred sites established before 1300 all but one small residential loci was abandoned before 1300. In contrast, all of the large habitation sites occupied after 1300, none were established before 1300.

This finding was correlated with a survey of the chronometrics surrounding the critical ware type (Salado or Roosevelt Redware particularly Gila Polychrome) in order to establish a baseline temporal context for the applicable seriations. We also used ceramic seriations from key chronometric sites; comparing these to those from the appropriate geographic/traditional areas. In the mid and late 90’s it was apparent that the bifurcations represented the boundary between the MWP and LIA, however direct causality was of course a spillover from the Great Drought (1275 -1295). Nonetheless, over the last decade its become increasingly more clear that we are looking at an extremely small aspect of a much larger cyclical climatic oscillation pattern.

We’re now in the process of writing a series of reports that includes a much larger and more focused data set which correlates ceramics with architectural and settle system patterns from a very large number of sites. Thus, I find Miller’s work intriguing. However, I’m also finding the mechanics as far as the radiocarbon sampling a bit difficult to follow. This is because I understand the C14 curve is extremely unreliable at this particular juncture due to rapid changes in the ratios of atmospheric gases. As I’m very much out of my depth here could someone here please explain how Miller established 1300 as the transit and how he has linked this boundary to volcanism?

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[…] PAGES2k expanded Kaufman’s 2009 network to 22 series, adding a number of new series, including Hvitavatn, Iceland, where Kaufman once again has used the data upside down to the interpretation of Gifford Miller, the original author and a very eminent paleoclimatologist. Miller’s report on Hvitavatn was previously discussed at CA here. […]